Response of plant diversity and soil physicochemical properties to different gap sizes in a Pinus massoniana plantation

As one means of close-to-nature management, forest gaps have an important impact on the ecological service function of plantations. To improve the current situation of P. massoniana plantations, three different sizes of forest gaps (large gaps, medium gaps and small gaps) were established to observe whether gap setting can improve the soil fertility and plant diversity of forest plantations. The results showed that compared with the control, the soil organic matter content of different soil layers increased significantly in the medium forest gap and large forest gap. The content of soil organic matter in the surface layer of the middle gap had the largest increase (80.64%). Compared with the control, the content of soil-available potassium between different soil layers decreased significantly by 15.93% to 25.80%. The soil hydrolysable nitrogen reached its maximum under the medium gap. Soil moisture showed significant changes among different gap treatments, different soil layers and their interaction, decreasing significantly in large gaps and small gaps but increasing significantly in medium gaps. The soil bulk density decreased significantly compared with the control, and the surface soil reached the minimum in the medium gap. There were different plant species in forest gaps of different sizes, and shrub layer plants were more sensitive to gap size differences than herb layer plants. The plant diversity indices of the shrub layer increased significantly and showed a maximum under the medium gap. The plant diversity of the herb layer showed the opposite trend, and the Shannon-Wiener index, Simpson index and Pielou index were significantly lower than those of the control. RDA showed that different gap treatments had significant effects on the distribution of plants under the forest. Soil available potassium, soil moisture and soil bulk density affected the distribution and diversity of plants under the forest, serving as the limiting factors of plant growth. In forest management, if we strictly consider the improvement of plant diversity and soil physicochemical properties, these results suggest that a medium gap should be established in a plantation for natural restoration.

Plantations on Forest Gaps and Edges Disturbs the Ecology of Threatened Understory Flora: A Case of Critically Endangered Gentiana Kurroo

Background: Within biodiversity hotspots, forest habitats have been disproportionately reduced and conservation efforts are insufficient, making restoration ventures extremely important. However, the impacts of restoration efforts on native threatened understory biodiversity residing in forest gaps and open edges have been seldom investigated. The current study attempts to fill this knowledge gap by investigating the ecology of a critically endangered understory plant namely Gentiana kurroo, across different successional stages of forest plantations including, open grassland (OG), 3-5-year-old plantation (YP), 5-15-year-old plantation (OP) and a mature forest (MF).Results: The highest population of the species was observed in OG, followed by YP, OP and MF. The regeneration was blocked by the plantation as evidenced by a ‘poor’ status in MF and OP, ‘fair’ at the YP and was ‘good’ only at OG. With an increase in canopy openness, the number of regenerating individuals increased, indicating the negative effect of the closed canopy on regeneration. The ordination projections show that the species density responds negatively with the stand basal area of the woody layer, litter depth, and tree density, but responds positively with soil organic carbon, available phosphorus, and reduction in the plantation. Conclusion: The present study suggests that plantations are more likely to benefit when established on degraded land rather than a replacement of the natural ecosystems, though those systems were initially forested or not. The results have significant implications in designing forest restoration programs, particularly on sites with a high diversity of threatened understory species. Thus, we propose that the forest restoration projects should be designed in a way that favours sensitive understory species without compromising the supply of timber and other non-timber forest products.

The effects of stump size and within-gap position on sprout non-structural carbohydrates concentrations and regeneration in forest gaps vary among species with different shade tolerances

Background To restore secondary forests (major forest resources worldwide), it is essential to accelerate the natural regeneration of dominant trees by altering micro-environments. Forest gaps are products of various disturbances, ranging from natural storms or wildfires to anthropogenic events like logging and slashing-and-burning, and sprouts of most tree species with non-structural carbohydrates (NSCs) storage can regenerate from stumps after gap formation. However, how the stump sprouts with diverse NSCs storages and stump sizes (i.e., diameters) adapt to various micro-environments of within-gap positions remains unclear. Therefore in this study, we monitored the stump sprout regeneration (density, survival, and growth) and NSCs concentrations of three dominant tree species with different shade tolerances and varying stump diameters at five within-gap positions for the first two consecutive years after gap formation. Results Stump diameter was positively correlated with sprout density, growth, and survival of all three tree species, but insignificantly related with sprout NSCs concentrations at the early stage after gap formation. The effect of within-gap position on sprout NSCs concentrations was different among species. After an environmental adaptation of two growing seasons, the north of gap (higher light availability and lower soil moisture habitat) was the least conducive for shade-intolerant Quercus mongolica to accumulate leaf NSCs, and the east of gap (shadier and drier habitat) was conducive to increasing the leaf NSCs concentrations of shade-tolerant Tilia mandshurica. Conclusions Within-gap position significantly affected leaf NSCs concentrations of all three tree species, but most of the sprout growth, survival, and stem NSCs concentrations were independent of the various within-gap positions. Besides stump diameter, the NSCs stored in stump and root systems and the interspecific differences in shade tolerance also contributed more in sprout regeneration at the early stage (2 years) of gap formation. A prolonged monitoring (> 10 years) is needed to further examine the long-term effects of stump diameter and within-gap position on sprout regeneration. All of these findings could be applied to gap-based silviculture by promoting sprout regeneration of dominant tree species with different shade tolerances, which would help accelerate the restoration of temperate secondary forests.